WABC-TV Channel 7 is plugging its huge hole left after tomorrow’s departure of Oprah Winfrey with news programming, starting with “First at Four” at 4 p.m. Thursday. Photo: AP

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WABC-TV’s decision to fight back against afternoon talk-show heavyweights “Ellen,” “Judge Judy” and “Dr. Phil” by expanding its 90-minute local newscast at 5 p.m. by one hour to 4 p.m. has some ad buyers scratching their heads.

The local ABC station, starting May 26, the first “Oprah”-free days on the station in 25 years, will present “First at Four,” a local newscast that certainly will not pull in Oprah Winfrey’s 6.5 million daily viewers — but hopes to make up for the smaller audience by being more profitable.

But that didn’t make sense to some on Madison Avenue.

“There’s only so much news you can put on,” Gary Carr, executive director with TargetCast, said in an interview yesterday. “It makes no sense to me to have news then at 5 p.m. and 6 p.m. and then national. How many murders and fires can you see at 4 p.m.?”

Brad Adgate, research director at Horizon Media, added: “How much are we just saturating viewers with local news?”

Some buyers would have liked WABC to replace “Oprah” with another syndicated show. Peter Gusmano, a managing partner at Group M, told The Post, “I think ultimately I would have liked to have seen that. They’re going to need it to push against people who would simply go to ‘Ellen.’ ”

But for WABC the decision to extend news is as much about cost saving as grabbing a piece of “Oprah”‘s $160 milion advertising booty, according to Kantar Media.

“Oprah” cost the station $60,000 an episode, or as much as $1.2 million a month, and while the large audience brought in buckets of advertising cash, the station had to share it with a syndication agent.

With the local news, it may be losing the $50,000 “Oprah” commanded for a local 30-second spot for something like $2,000 a spot during its local news, but it gets to keep all of the fewer ad dollars that roll in.

And producing an hour of news isn’t quite as pricey as buying “Oprah.”

Plus, the extra hour of news may not be forever.

ABC is expected to conclude a deal with Katie Couric once her contract with CBS expires in early June.

Couric’s show, penciled in for September 2012, is expected to be slotted anywhere between 3 p.m. to 5 p.m. on stations.

The 3 p.m. slot is currently occupied by soap, “General Hospital,” a show whose fate seems uncertain given ABCs recent decision to dump two other soaps.

Adgate saw a bit of WABC-TV’s logic.

ABC, he said, was at least offering a different genre of programming to its counterparts.

“The downside is they don’t get the “Oprah,” ratings or the lead-in, but news is so habit-forming they’re counting on creating that [at 4 p.m.],” he said.

Carr added: “Some of those ratings will leave broadcast TV altogether. ” ‘Ellen,’ ‘Dr. Oz’ and ‘Dr. Phil,’ will try to get the ‘Oprah’ money.”

“Eyewitness News First @ 4 PM,” will face off against “Judge Judy,” on CBS2; “Ellen,” on NBC4 and Oprah spin-off “Dr. Oz,” on Fox5 in the New York market. Elsewhere around the country, other ABC stations are also programming news, while other stations are slotting Dr. Oz.